This invention relates to integrated circuit packages; and more particularly, it relates to methods of cutting input/output columns on an integrated circuit package to a predetermined length.
In the prior art, integrated circuit packages have been disclosed which include a body that completely encloses an integrated circuit chip and include multiple input/output columns which extend perpendicularly from the body. Each input/output column is connected by microscopic conductors within the body of the integrated circuit package to the integrated circuit chip, and thus the input/output columns provide the means by which electrical signals are sent to and received from the chip.
One method of casting the input/output columns on the body of the integrated circuit package is described in the prior art in U.S. Pat. No. 5,454,159. In that patent, FIGS. 6 and 7 illustrate a template which has a plurality of cylindrical-shaped holes that provide a pattern for the input/output columns. This template is placed on the body of the integrated circuit package such that the holes of the template are aligned with locations on the body of the package where the input/output columns are to be formed. Then the holes in the template are filled with solder balls, and the assembly of the template on the body of the package is sent through a belt furnace where the solder balls are melted and resolidified.
After the input/output columns have been formed on the integrated circuit package as described above, they can be connected to a printed circuit board by soldering the open ends of the input/output columns to respective I/O pads on the printed circuit board. In this step, the solder which is used has a lower melting temperature than the solder balls from which the columns were made so that the columns stay in a solid state.
However, prior to such a soldering step, all of the input/output columns can be cut to a predetermined length. Such a cutting operation is performed to trim all of the input/output columns to the same length and thereby insure that the ends of all of the input/output columns make contact with their corresponding I/O pads on the printed circuit board.
In the prior art, an apparatus which has been used to cut the input/output columns on an integrated circuit package is shown in FIG. 1. This apparatus includes a shear plate 10 and a blade 11. The shear plate 10 has a plurality of holes 10a which match the pattern of the input/output columns on the integrated circuit package; and those columns are passed through the holes 10a as shown in FIG. 1. Then to cut the input/output columns, a surface 11a of the blade is placed flush against the surface of the shear plate 10 from which the input/output columns extend; and while the blade is held in that position, the blade is slid against the shear plate through the input/output columns.
However, a problem with the FIG. 1 apparatus is that at a microscopic level, surface 11a of the blade inherently has a certain degree of roughness; and similarly, the surface of the shear plate from which the input/output columns extend also has a certain degree of roughness. Consequently, a small gap inherently exists between the blade 11 and the shear plate 10.
Thus, when the blade 11 is pushed through the input/output columns, a small amount of debris from the columns can get caught in the gap between the blade and the shear plate. This debris will build up as a smear on surface of 11a of the blade while each input/output column is cut. In turn, this smear produces defects in the cut ends of the columns such as those which are shown in FIGS. 5 and 6 and which are described in detail in the "Detailed Description."
Accordingly, a primary object of the invention is to provide an improved method of cutting the input/ouput columns on an integrated circuit package by which the above defects are eliminated.